Method of preparing barium silicate phosphor



Patented May 20, 1952 UNITED STATES OF FlC-E METHOD OF PREPARING BARIUMSILICATE PHOSPHOR poration of New York No Drawing. Application March 22,1950, Serial No. 151,320

'7 Claims. (01. 252-2014) My invention relates generally to fluorescentmaterials or phosphors and more particularly to barium silicatephosphors. Still more particularly, my invention relates to a method ofpreparing phosphor of barium disilicate activated with lead(BasizOs-Pb).

This application is a continuation-impart of my copending patentapplication Serial No. 110,477, filed August 15, 1949, now abandoned,and assigned to the assignee of the present apvplication.

Such phosphor gives good results when em ployed influorescent lamps ofthe low pressure mercury vapor type, and emits ultraviolet radiations oflonger wavelength when excited by short ultraviolet radiations of themercury vapor discharge. However, it is difficult to produce,particularlyv on a large scale. The phosphor may be produced bypreparing a mixture of suitable proportions of barium carbonate, silicaand lead fluoride, ball-milling the mixture with water, drying, andfiring at a temperature of about 1100 C. This process produces a fairlysatisfactory material but requires a firing period as long as '24 hoursand also requires wet mixing of the raw materials.

An object of my invention is to provide a method which permits shorterfiring time, as well as complete dry handling of the ingredients, and

which produces phosphors of high efficiency, even 5.

higher than obtained heretofore.

According to the present invention, I have'discovered that when the.phosphor ingredients are fired with "a catalyst consisting of acombination of fluoride and chloride the combination is much :1

proportion of a lead compound. As sources of barium and silicon I mayemploy the oxides or materials which, upon heating, break down to yieldthe oxides. Similarly, various compounds may be employed as the sourceof the lead activator. As sources of fluorine and chlorine I prefer toemploy barium fluoride and barium chlo ride, preferably in a totalamount of 2-12 mol per cent of the barium silicate, and preferably inabout equal proportions although a mol ratio of (112? within the rangeof about 0.2:2 to 2:0.2

may be used. However, good results have also been obtained with ammoniumfluoride and chloride in equivalent amounts. Also useful are thefluoride and chloride of calcium in equivalent amounts. Other fluorideswhich may be used are: PbF2, NI-IrF or NH4HF2. Other chlorides whichalso proved to be eifective are SrC12,MgC12, A1C13 and ZIlC12, likewisein equivalent amounts. This was surprising because phosphors in which 50mol per cent of the barium were replaced with Ca, Sr, Mg, Be or Li wereof low brightness. Yet, when the chlorides of these elements were usedfor refiring the material, which had been previously fired with afluoride catalyst, in amounts of about 5 mol per cent of the barium,phosphor brightness was either unchanged or only slightly reduced.Moreover, the result was unexpected because the same technique appliedto phosphor of calcium silicate activated with lead and manganese gavepoor results when using halides other than those of calcium andammonium.

Substantially the same results were obtained when the amount of BaFz inthe original mixture was either doubled or halved, and when the amountof barium chloride was lowered to 1 per cent or increased to 8 per cent,and when the firing temperature was raised to 1150 C..or .lowered to1050 C. for either the first or the second fire, or for both. The finalchoice of composition and firing temperature depends upon the size anddimensions of the powder chargeand the furnace. .Neither of them arevery critical. They must be so adjusted by trial and error that thefinest particle size powder of good working characteristics and lampperformanceis obtained. In general, firing temperatures of about1000-1200 C. may be employed.

When the material was used in a low pressure mercury vapor lamp, theinitial output was about 131 relative units of energy compared withabout 104 units for lamps containing phosphor prepared by the priormethod referred to above. When about to 5 per centof CaClz-ZHzO was usedin the refiring step in place of .BaClz the efliciency was onlyinsignificantly lower, averaging 129 .as against v131 units above. X-rayinvestigation hasindicated that the material prepared with CaClz is anew composition-of matter, namely, a lead activated barium-calcium-disilicate. Identity ofXeray patternsforBaSizOa and (Ba, Ca) Si205,respectively, has shown that (has CaSlzOs seems to form a solid solutionwith BaSizOs in amounts not exceeding about 5-7 mol .per cent, eventhoughnormally acompound of compositionCaSizOa does not exist.

The material may also be prepared by a single firing method wherein boththe fluorine and chlorine catalysts are present in the original mixture.However, the double firing method produces the brightest phosphors inthe shortest firing time and has proved to be more reproducible andconvenient for larger scale production than the single firing method.

Example I By way of example, the phosphor may be prepared as follows: Amixture of 300 grams BaCos 240 grams silicic acid (containing about 10per cent water), 12 grams PhD and 13.5 grams BaFz is ball-milled dry forabout 1% hours, and then fired on open silica trays in alead-conditioned furnace at 1100 C. for 2 hours. When cold, the mass isagain ball-milled dry with about 4 to 5 per cent of the weight ofBaClz-ZHzO for an hour, and refired at 1100 C. for 2 hours. When cold,the phosphor is screened and is then ready for use.

Example II A mixture of 300 grams BaCO3, 240 grams silicic acid(containing about per cent H) and 13.2

tion PbOBaFz, this replacement may be made on the basis of either the Pbor the F content of the mixture, or by employing both Pb and F. With amol for mol replacement PbFz for PbO, (omitting any BaFz). the amount offluorine in the mixture will be about 40 per cent lower than that statedin Example I. With a mol for mol replacement of PbFz for BaFz, (omittingany 'PbO), the amount of Pb in the mixture will be about 40 per centhigher than in Example I. Example II represents the situation in whichPbFz replaces all the PbO, omitting BaFz.

The amounts of the fluoride and chloride catalysts are about 5 mol percent each of the BaSizOs base.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing compounds of barium and siliconwhich upon heating will react to form barium disilicate with anactivating proportion of a lead compound, and firing the mixture at atemperature of approximately 1000-l200 C. with additions of catalystconsisting of both a fluoride and a chloride, the fluoride being of thegroup consisting of fluorides of barium, ammonium, lead and calcium, andthe chloride being of the group consisting of chlorides of barium,ammonium, calcium, strontium, magnesium, aluminum and zinc, the saidcatalysts being in a total amount of about 2-12 mol per cent of thebarium disilicate with a mol ratio of fluorine to chlorine between about0.2:2 and 2:02.

2. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing compounds of barium and siliconwhich upon heating will react to form barium disilicate with anactivating proportion of a lead compound, and firing the mixture at atemperature of approximately 1000-1200 C.

with additions of catalyst consisting of both a fluoride and a chloride,the fluoride consisting of barium fluoride and the chloride being of thegroup consisting of chlorides of barium, ammonium, calcium, strontium,magnesium, aluminum and zinc, the said catalysts being in a total amountof about 2-12 mol per cent of the barium sili- V cate with a mol ratioof fluorine to chlorine between about 0.2:2 and 2:02.

3. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing compounds of barium and siliconwhich upon heating will react to form barium disilicate with anactivating proportion of a lead compound and with a fluoride catalyst ofthe group consisting of fluorides of barium, ammonium, lead and calcium,heating the mixture at a temperature of about 1000-1200 C. for about 2hours, remixing the resultant product with a chloride catalyst of thegroup consisting of chlorides of barium, ammonium, calcium strontium,magnesium, aluminum and zinc and refiring at a temperature of about1000-1200 C. for about an hour, the said catalysts being in a totalamount of about 2-12 mol per cent of the barium disilicate with a molratio of fluorine to chlorine between about 0.212 and 220.2.

4. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing carbonate and silicate inproportions to form barium disilicate with an activating proportion oflead oxide and with barium fluoride, heating the mixture at atemperature of about 1000-12000 C. for about 2 hours, remixing theresultant product with barium chloride and refiring at a temperature ofabout 1000- 1200 C. for about an hour, the amounts of the bariumfluoride and chloride each being about 5 mol per cent of the bariumdisilicate base.

5. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing barium carbonate and silica inproportions to form barium disilicate with an activating proportion oflead oxide and with barium fluoride, heating the mixture at atemperature of about 1000-1200 C. for about 2 hours, remixing theresultant product with ammonium chloride and refiring at a temperatureof about 1000-1200 C. for about an hour, the amounts of the bariumfluoride and ammonium chloride each being about 5 mol per cent of thebarium disilicate base.

6. The method of preparing a fluorescent composition of lead activatedbarium disilicate which comprises mixing barium carbonate and silica inproportions to form barium disilicate with an activating proportion oflead oxide and with barium fluoride, heating the mixture at atemperature of about 1000-1200 C. for about 2 hours, remixing theresultant product with calcium chloride and refiring at a temperature ofabout 1000-1200 C. for about an hour, the amounts of the barium fluorideand calcium chloride each about 5 mol per cent of the barium disilicatebase.

7. The method of preparing a fluorescent composition of lead-activatedbarium disilicate which comprises mixing barium carbonate and silica inproportions to form barium disilicate with an activating proportion oflead oxide and with barium fluoride, heating the mixture at atemperature of about 1000-1200 C. for about 2 hours, remixing theresultant product with a chloride catalyst of the group consisting ofchlorides of barium, ammonium, calcium, strontium, mag- 5 nesium,aluminum and zinc and refiring at a temperature of about 1000-1200 C.for about an hour, the amounts of the barium fluoride and the chloridecatalyst each being about 5 mol per cent of the barium disilicate base.

HERMAN C. FROELICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number Number 6 UNITED STATES PATENTS Name Date Butler Oct. 25, 1949Schulman Feb. 14, 1950 Ginther Feb. 28, 1950 FOREIGN PATENTS CountryDate Great Britain Apr. 14, 1942

1. THE METHOD OF PREPARING A FLUORESCENT COMPOSITION OF LEAD ACTIVATEDBARIUM DISILICATE WHICH COMPRISES MIXING COMPOUNDS OF BARIUM AND SILICONWHICH UPON HEATING WILL REACT TO FORM BARIUM DISILICATE WITH ANACTIVATING PROPORTION OF A LEAD COMPOUND, AND FIRING THE MIXTURE AT ATEMPERATURE OF APPROXIMATELY 1000-1200* C. WITH ADDITIONS OF CATALYSTCONSISTING OF BOTH A FLUORIDE AND A CHLORIDE, THE FLUORIDE BEING OF THEGROUP CONSISTING OF FLUORIDES OF BARIUM, AMMONIUM, LEAD AND CALCIUM, ANDTHE CHLORIDE BEING OF THE GROUP CONSISTING OF CHLORIDES OF BARIUM,AMMONIUM, CALCIUM, STRONTIUM, MAGNESIUM, ALUMINUM AND ZINC, THE SAIDCATALYSTS BEING IN A TOTAL AMOUNT OF ABOUT 2-12 MOL PER CENT OF THEBARIUM DISILICATE WITH A MOL RATIO OF FLUORINE TO CHLORINE BETWEEN ABOUT0.2:2 AND 2:0.2.